One effective method for inspecting and monitoring various structures is guided wave testing (GWT) using magnetostrictive sensor (MsS) technology. The principle of magnetostriction is based on either shifting or oscillation/rotation between magnetic domains in the material due to applied magnetic fields. Typically, a permanent magnetic field is used to give the domains a preferred orientation. Variable magnetic fields are also applied to initiate the rotation of the domains causing the dimensional changes. Depending on the mutual orientation (in-plane or out-of-plane) and on the mutual magnitude of the magnetic fields, oscillation of domains can produce longitudinal or transverse vibrations.
There are many applications of MsS testing, with testing of plate structures being a common application. Examples of industries having a need for testing large plates welded together are refineries, chemical plants, and electric power generation plants.
For guided waves testing of plates, a plate type of Mss sensor can be used, herein referred to as a “MsS plate sensor”. However, with conventional MsS plate sensors, a series of incremental movement of the sensor across the surface of the plate is required to cover the large surface.
To maximize coverage of MsS plate sensors, directional sensors have been developed. U.S. patent application Ser. No. 15/376,049, to Vinogradov, et al., entitled “Non Destructive Magnetostrictive Testing with Unidirectional Guided Waves Generated by Ferromagnetic Strip Sensor” describes various embodiments of a directional MsS sensor. A number of unidirectional MsS sensors are arranged in a circular configuration, which is placed on the plate to be tested. Each MsS sensor tests a segment of the plate.